package org.webframe.beetlsql;

/**
 * twitter的snowflake算法 -- java实现
 *
 * @author beyond
 * @date 2016/11/26
 */
public class Snowflake {

    /**
     * 起始的时间戳
     */
    private final static long START_STMP = 1480166465631L;

    /**
     * 每一部分占用的位数
     */
    //序列号占用的位数
    private final static long SEQUENCE_BIT = 12;
    //数据中心占用的位数
    private final static long DATACENTER_BIT = 5;

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long DATACENTER_LEFT = SEQUENCE_BIT ;
    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
    //数据中心
    private long datacenterId;
    //序列号
    private long sequence = 0L;
    //上一次时间戳
    private long lastStmp = -1L;

    public Snowflake(long datacenterId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
    }

    /**
     * 产生下一个ID
     *
     * @return
     */
    public synchronized long nextId() {
        long currStmp = getNewstmp();
        if (currStmp < lastStmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastStmp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStmp = currStmp;

        return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                | datacenterId << DATACENTER_LEFT       //数据中心部分
                | sequence;                             //序列号部分
    }

    private long getNextMill() {
        long mill = getNewstmp();
        while (mill <= lastStmp) {
            mill = getNewstmp();
        }
        return mill;
    }

    private long getNewstmp() {
        return System.currentTimeMillis();
    }

    public static void main(String[] args) {
        Snowflake snowFlake = new Snowflake(2);
        Long id=snowFlake.nextId();
        System.out.println(id);
        System.out.println(id.toString().length());
        System.out.println(Long.toBinaryString(id));
        int maxTimes = 1000 * 10000;
        long start = System.currentTimeMillis();
        for (int i = 0; i < maxTimes; i++) {
            snowFlake.nextId();
        }
        long end = System.currentTimeMillis();
        System.out.println("预热"+maxTimes+" 平均:"+maxTimes / (end - start)+"/毫秒");

        long start1 = System.currentTimeMillis();
        for (int i = 0; i < maxTimes; i++) {
            snowFlake.nextId();
        }
        long end1 = System.currentTimeMillis();
        System.out.println("正式"+maxTimes+" 平均:"+maxTimes / (end1 - start1)+"/毫秒");

    }
}
